The focus of this project is on the analysis of quantitative trait loci (QTLs) associated with length of life, or longevity, as a phenotype of aging. Although previous findings suggest that the upper range of heritability of longevity is about 0.30, the findings from these studies may be confounded by viral pathogens and so indicate genetic predisposition to disease rather than longevity. In this study, a pathogen-free barrier environment will be provided for 480 animals (10 males and 10 females, each of 22 RI stains and 2 progenitor strains) throughout their lives. In order to follow future post-mortem examination, animals will be examined at regular intervals throughout the day to retrieve individuals within a short time of expiration in order to prevent or minimize autolysis. QTL analysis based on the RI strain means will relate longevity to the genotypic strain distribution patterns. An advantage of the fixed genotype of the RIs is that it will allow relationships to be adduced between the biomarker phenotypes measured in other RI samples to that of longevity, providing correlation between the marker variables and length of life.